Japanese Patent Application Laid-Open (JP-A) No. 63-045444 discloses that the exhaust gas temperature can be detected in order to protect an exhaust system component. Specifically, when the temperature increases excessively, the fuel feed rate is increased and corrected to decrease the exhaust gas temperature.
JP-A 2004-177179 discloses that an internal resistance (impedance) of a sensor element of an air/fuel (A/F) ratio sensor (oxygen sensor) arranged in an exhaust system can be measured and used to estimate the temperature of the exhaust gas.
In both JP-A 63-045444 and JP-A 2004-177179, the fuel feed rate is increased when the exhaust gas temperature reaches a predetermined temperature. However, the temperature increase of the exhaust manifold or other similar elements that have a large heat capacity lags behind the increase in the exhaust gas temperature. Increasing the fuel feed rate immediately after the exhaust gas temperature reaches a exhaust system components occurs and can therefore reduce the fuel efficiency of the engine.